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lect_2sep29f09

# lect_2sep29f09 - Outline#2 29-SEP-2009 1 Review...

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1 Outline #2 29-SEP-2009 1. Review Calculations-Units & Sig Figs examples 2. Atomic Theory Background (Mass Laws),Dalton 3. Atomic Structure Electrons, Nuclei, protons, neutrons (Thompson, Milliken, Rutherford, Chadwick)

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2 Sig Fig Rules (Review) 1. Significant: Nonzero digits Trailing zeroes followed by decimal Trailing zeroes to right of decimal 2. Not significant: Zeros only identifying decimal point. Ex: (a) 0.0790 = 7.90*10 -2 . (3 sig figs) (b) 120. = 1.20* 10 2 (4 sig figs) (c) 12000 = 1.2*10 4 (2 sig figs)
3 3. Rounding Off: a. If last digit > 5 , increase previous digit by 1. Ex: Round 2.346 to 3 sig figs so 2.35 a. If last digit < 5 , keep previous digit. Ex: Round 2.344 to 3 sig figs so 2.34 c. If last digit = 5, increase previous digit by one if odd else keep previous digit if even. Ex: Round 2.355 to 3 sig figs so 2.36 Ex: Round 2.345 to 3 sig figs so 2.34 Sig Figs Rules (cont.)(Review)

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4 Sig Fig Rules (cont.)(Review) 4. Exact number - number from counting items or defining a unit. Ex: nine coins means exactly 9. Ex: Twelve inches per foot means exactly 12. Exact numbers do not effect # sig figs in calculated result. (As if exact number has ∞ # sig figs!)
5 Sig Fig Rules (cont.) (Review) Sig figs in calculated numbers 5. multiplying & dividing – keep same # sig figs as in factor with least # sig figs. Factor –number multiplied or divided. 6. adding & subtracting- give same number of decimals as in term with least power of ten. Term- number added or subtracted. 7 . Multistep Calculations- carry one or two additional figures then round off after final step.

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6 Review: Sig Figs Give number of sig figs in: a. 0.07300 g 4 sig fig b. 5.03 kg (express in g also) 3 sig fig d. 0.008095 m 3 sig fig e. 2.5*10 -3 m 2 sig fig
7 Review: Sig Figs ( started last time ) 1.546 g - 0.65 g = ? 1.546 g + 0.65 g = 2.196=> 2.20 0.71+81.8 = 82.5=> (847.89-847.73)*14673=>0.16 x 14673=2347.68 2.3x 10^3

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8 REVIEW: Sig Figs Refer to Rules 1. How many sig figs in a. 0.0500? (scientific notation?)2 sf 5X10x10^-2 b. 13000 (scientific notation?) 2sf 1.3x 10^4 c. 6030. (scientific notation?)4sf 2. Give results in proper # of sig figs a. 1.2*6.000= 7.2 b. 6.000-1.2 =4.8 3. Round to 4 sig figs. 231.554=231.6
9 Name________ Sample Quiz 2 TA__________ 1.(2) How many sig figs are in: a. 2100? 2sf b. 0.0035? 2sf c. answer to 9*0.12345 (9 is exact)? 5 sf 2. (1) Express the answer to this with proper # of sig figs. 12.5*4.637= 54.5875 =54.6 3. (1) Express the answer to this with proper # of sig figs.

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